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Unix Access Privileges. Who can access what files and how. Access privileges. All unix files have privileges associated with them. These privileges determine who can access the file. These privileges determine how people can access the file. Viewing access privileges.
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Unix Access Privileges Who can access what files and how.
Access privileges • All unix files have privileges associated with them. • These privileges determine who can access the file. • These privileges determine how people can access the file.
Viewing access privileges • Use the ls -l command. drwx------ 2 jimd 8192 Jul 12 12:26 nsmail/ -rw-r--r-- 1 jimd 945 Mar 15 16:01 old.cshrc -rwxrwxrwx 1 jimd 168 Jan 13 1998 file.exe -rw-rw-rw- 1 nobody 382 Nov 18 1998 old.profile -rw------- 1 jimd 652 Jul 12 12:16 old.xsession drwx------ 2 jimd 8192 Jun 23 13:21 thesis/ -rw-r--r-- 1 jimd 1186776 Jul 13 15:07 win32tutorial.ps Access Privileges
Types of file access • Read — person can look at the contents of the file. • Write — person can change the file. • Execute — person can execute the file (applies only to directories and program).
Types of users • User/owner -- the person who owns/created the file. • Group — Unix allows for the creation of groups. • Others/world -- everyone else in the world that has access to that computer.
To change permissions chmod — changes the access mode of a file. Two methods exist symbolic absolute
chmod - symbolic chmod uses the following notation: u user (owner) of the file g group o others (public) a all (owner, group, and public) = assign a permission + add a permission - remove a permission
Examples: To give the owner execute permission without changing any other permissions: chmod u+x filename To remove read and write permissions from group members: chmod g-rw filename
chmod - absolute • Absolute - you specify a numeric equivalent for a set of permissions. • You specify all permissions at once.
chmod - absolute • chmod [xxx] [file] • Where each x is some number from 0 - 7. • Each number specifies a level of privileges for a specific group.
chmod - absolute • e.g., chmod 644 moocow.txt User permission World permission Group permission
chmod - absolute • Permissions: rwx • Read = 4 - 100 • Write = 2 - 010 • Execute = 1 - 001 • Set permissions by adding the values of all the permissions you wish to set.
chmod - examples • To give yourself read & write permission and no permission to anyone else: • chmod 600 foobar.txt • To give yourself read & write permission and everyone else read permission only: • chmod 644 index.html • To give yourself full access to a directory, and everyone else read & execute permission only: • chmod 755 homeDirectory
